Overtemperature and lubricant loss protector for compressors



D. N. SHAW Feb. 11, 1969 OVERTEMPERATURE AND LUBRICANT LOS S PROTECTOR FOR COMPRESSORS Filed Dec. 2, 1966 FIG. 2

INVENTOR. DAVID N. SHAW.

ATTORNEY.

United States Patent OfiFice 3,426,962 Patented Feb. 11, 1969 3 Claims ABSTRACT OF THE DISCLOSURE Lubricant heater and protector for compressor including a heater, a switch actuator heated by heater and a normally closed switch in compressor circuit. Upon predetermined increase in temperature indicating loss of lubricant, switch opens to prevent compressor operation.

This invention relates to compressor lubrication systems, and more particularly, to a control for protecting compressors against overtemperatures and loss of lubri' cant.

Where compressors, particularly hermetic type compressors, are used in refrigeration system applications, the extra cost for a heater to warm the compressor lubricant when the compressor is shut down can be justified on the need to prevent, or at least inhibit, migration of the system refrigerant into the compressor lubricant. While the desirability of protecting compressors against total or substantial loss of lubricant is recognized, the probability of loss of lubricant is not so great as the probability, indeed almost certainty, that refrigerant will migrate into the lubricant during the compressor ofi? cycle if the lubricant is not heated. Hence, the cost in providing some type of lubricant loss protection is not normally thought to be justified, and this form of compressor protection is usually foregone.

It is a principal object of the present invention to provide a new and improved compressor lubrication system.

It is an object of the present invention to provide a combination lubricant heater and compressor overtemperature protector.

It is a further object of the present invention to provide an improved compressor lubricant heater incorporating a control means which renders the compressor inoperative when the supply of compressor lubricant is below a safe level.

It is an object of the present invention to provide, in conjunction with a compressor lubricant heater, a control means responsive to temperatures of the heater effective at a predetermined heater temperature to render the compressor inoperative.

This invention relates to a combination lubricant heater and protector for a compressor comprising in combina tion, means for heating the compressor lubricant; and means for protecting against loss of lubricant and excessive compressor operating temperatures including a control switch adapted to be arranged in the energizing circuit to the compressor so that actuation of the control switch interrupts the energizing circuit to the compressor to render the compressor inoperative, and means responsive to temperature conditions of the lubricant heating means adapted at a predetermined temperature to actuate the control switch.

Other objects will be apparent from the ensuing description and drawings in which:

FIGURE 1 is a view partially in section of a compressor incorporating the combination lubricant heater and lubricant loss protector of the present invention; and

FIGURE 2 is a wiring diagram for the compressor shown in FIGURE 1.

Referring to the drawing, there is shown a compressor 10 incorporating the combination lubricant heater and low oil level protector 45 of the present invention. It is understood that the combination heater-protector 45 may be employed in other compressor constructions.

Compressor 10 comprises a vertical unit with a motor 14 encased in housing 15 and compression means 16 above motor 14 and operatively connected to rotor 17 of motor 14 by crankshaft 18. Oil sump 20 of compressor 10 is above compression means 16. In this construction, motor housing 15 forms a base supporting compressor 10.

Compression means 16 includes cylinder block 22 sealingly secured to motor housing 15 to form with housing 15 and sump cover 20' a hermetic or sealed unit. Cylinder block 22 has one or more cylinders 23 within which pistons 24 are movably disposed. Cylinder head 25, having valve controlled suction and discharge manifolds 26, 27 respectively, is suitably secured to cylinder block 22 opposite cylinders 23. Suction manifold 26 in cylinder head 25 connects with suction passage 29 in block 22. Passage 29 opens into motor compartment 30. Discharge manifold 27 in head 25 connects with discharge line 32. Check valve 33 in discharge line 32 prevents backflow of pressure fluid into compressor 10.

Connecting rod 35 operatively connects eccentric 18' of crankshaft 18 with piston 24. The motor end of crankshaft 18 has rotor 17 of motor 14 suitably fixed thereto.

The pump end of crankshaft 18 is operatively connected to a suitable oil circulating pump 36. Cover 20' is tightly secured to upper face of cylinder block 22 to form, in cooperation therewith oil sump 20. Oil inlet line 38 for pump 36 has check valve 39 to prevent reverse fluid flow in inlet line 38.

Oil from pump 36 flows through crankshaft feed passage 60 to the various points of frictional wear in compressor 10 such as crankshaft journals connecting rods, etc. Return oil accumulates in crankcase 12.

An opening (not shown) in motor housing 15 adjacent the base thereof communicates compressor 10 with the source of gas to be compressed, the entering gas passing through motor compartment 30 in and around motor 14 to cool motor 14, and through suction passage 29 and suction manifold 26 into cylinder 23. Discharged gas from discharge manifold 27 passes into discharge line 32.

Oil accumulating in crankcase compartment 12 returns to sump 20 through combination pressure bleed and oil return line 40. A second pressure bleed line 42 is disposed between sump 20 and the suction side of compressor 10, as for example, suction passage 29. Valve 41 in line 40 closes line 40 when compressor 10 is shut down. Check valve 43 in line 42 prevents reverse flow of pressure gas from suction passage 29 through line 42 in sump 20.

On shutdown of compressor 10, sump 20 is effectively isolated from both crankcase compartment 12 and suction manifold passage 29 by valves 39, 41, 43, and the migration of refrigerant into the body of oil in sump 20 is effectively prevented. During the life of the compressor, wear on valves 39, 41, 43, particularly check valves 39, 43, may result in leakage of refrigerant into oil sump 20.

To prevent contamination of the lubricant in sump 20 should refrigerant leak past valves 33, 41, or 43, a heater 48, combined with a lubricant loss and compressor overtemperature protector as will be more apparent hereinafter, is provided.

The combination heater-lubricant loss protector, designated generally by numeral 45, comprises an elongated generally cylindrical element having a base 46 with housing 47 encasing heater 48. Heater 48 may for example comprise a resistor. Base 46 of the combination heaterprotector 45 is sealingly fixed in wall 20' of sump 20 with housing 47 thereof projecting into sump 20. Heater-protector 45 is arranged in sump 20 below the normal lubricant level and at a level representing the minimum amount of lubricant deemed necessary for adequate compressor lubrication.

A thermal type switch actuator 50, which is preferably encased in housing 47, is arranged in close proximity to heater 48. Thermal actuator 50 comprises a suitable thermal or heat sensitive mass movable in accordance with changes in temperature of the heater 48. Normally closed control switch 52 is operatively connected to actuator 50, the actuator 50 being adapted to open switch 52 at a predetermined high temperature condition of heater 48. Switch 52 is preferably of a type requiring manual reclosing.

Referring to FIGURE 2, motor 14 of compressor is energized from a suitable source of electrical energy, represented by leads L L through contact 54. A control circuit, connected to leads L L through contact 54. A control circuit, connected to leads L L through step down transformer 55, includes contactor coil 56, switch 52 and control switch 57 series connected across the secondary Winding 55, of transformer 55. Heater 48 of the combination heater-protector 45 is connected across winding 55' of transformer 55.

When compressor 10 is operated, control switch 57 is closed to complete, through switch 52, an energizing circuit to contactor coil 56 which in turn closes contact 54 to complete the energizing circuit to the compressor driving motor 14. On opening of control switch 54, the circuit to relay 56 is interrupted permitting contact 54 to open and de-energize compressor driving motor 14.

Heater 48 of the combination heater-protector 45, which is energized from leads L L through transformer 55, continually warms the lubricant in sump 20.

The effectiveness of heater 48 of the heater-protector 45 in heating the lubricant in sump depends upon the quantity of lubricant or lubricant-refrigerant mixture in sump 20. Where the level of lubricant in sump 20 is such that housing 47 of heater-protector is substantially covered by relatively cool lubricant, the heat generated by heater 48 is absorbed by the lubricant and the temperature of the heater 48 remains relatively low, where, however, the level of lubricant is such that housing 47 is uncovered or only partially covered by fluid in sump 20, the temperature of heater 48 rises. Thermal element 50, disposed proximate heater 48 in housing 47, responds to the rise in temperature of heater 48 and at a predetermined temperature opens switch 52 interrupting the energizing circuit to contactor coil 56 and thereby shutting down compressor 10.

Where operating temperatures of compressor 10 rise to an abnormaly high level, the temperature of the lubricant in sump 20 rises. As lubricant temperatures rise, the temperature level of heater 48 rises and thermal actuator 50, at the predetermined response temperature thereof, opens switch 52 to interrupt the energizing circuit to contactor coil 56 and shut down compressor 10.

While control switch 52 and thermal actuator 50 therefor are combined in a housing 47 with lubricant heater 48 to form a unitary heater-protector unit 45, it is understood that control switch 52 and actuator 50 thereof may be separate from the heater assembly. In that event, actuator 50 is arranged proximate heater 48 and in heat exchange relation therewith.

I claim:

1. In combination, means for heating the lubricant of a compressor; and means for protecting said compressor against loss of lubricant and excessive operating temperatures including a normally closed control switch adapted to be arranged in the energizing circuit to the compressor so that actuation of said control switch interrupts the energizing circuit to the compressor to render said compressor inoperative, and means responsive to temperature conditions of said lubricant heating means adapted at a predetermined increase in temperature to open said control switch.

2. The combination according to claim 1 in which said heating means includes a sealed housing adapted to project within the lubricant sump of the compressor, and a heating element encased in said housing; said temperature responsive means including a thermal powered operator for said control switch in said housing and in heat exchange relation with said heating element, said thermal powered operator being adapted to open said control switch and render said compressor inoperative at said predetermined temperature.

3. The combination according to claim 2 in which said heating means housing is arranged in said compressor sump at a predetermined lubricant level.

References Cited UNITED STATES PATENTS 2,199,426 5/1940 Coolfert 184-6 2,629,041 2/1953 Fein et a1 184-104 2,768,708 10/1956 Cooper 184-6 2,939,687 6/1960 Goettl 10325 3,107,843 10/1963 Finn 230-6 WILLIAM L. FREEH, Primary Examiner.

US. Cl. X.R. 

